1. Field
The present invention relates to a technique for an optical scanning device, an image display device provided with an optical scanning device, a retinal scanning display, and a driving method of an optical scanning element, and more particularly to a driving technique for an optical scanning element.
2. Description of the Related Art
Conventionally, with respect to an optical scanning device which scans light, there has been known an optical scanning device which scans light using a resonance-type optical scanning element. With respect to the resonance-type optical scanning element, as described in JP-A-2005-275198, there has been known an optical scanning element which includes a mirror portion having a reflection surface, and an oscillating body which is connected to the mirror portion and includes a spring portion which generates torsional oscillations thus capable of performing resonance oscillations of the mirror portion in a swinging state. Here, light which is incident on the optical scanning element due to the resonance oscillations of the mirror portion is scanned on the reflection surface.
In this kind of optical scanning device, optical scanning is performed by making use of the resonance oscillations generated at the time of torsional oscillations of the oscillating body. However, the oscillating body is considered to generate subsidiary resonance oscillations besides the torsional oscillations. As such subsidiary resonance oscillations, a phenomenon in which the mirror portion of the oscillating body oscillates in a direction parallel to the reflection surface, that is, the lateral oscillations, a phenomenon in which the mirror portion of the oscillating body oscillates in a direction perpendicular to the reflection surface, that is, longitudinal oscillations and the like are named.
However, when the resonance frequency of the torsional oscillations and the resonance frequency of the subsidiary oscillations agree with each other or are arranged close to each other, even when the oscillating body is oscillated with frequency equal to the resonance frequency of the torsional oscillations, the subsidiary oscillations are superposed on the torsional oscillations in the oscillating body. When the superposition of the subsidiary oscillations on the torsional oscillations occurs along with the oscillations of the oscillating body, an oscillation state of the reflection surface of the mirror portion is deviated from a target oscillation state and hence, the characteristics of optical scanning are also deviated from target characteristics. Accordingly, the optical scanning element is designed such that the resonance frequency of torsional oscillations and the resonance frequency of subsidiary oscillations do not come close to each other.